Control of drop printing

ABSTRACT

A high speed ink jet printing apparatus for printing on a record medium moving along a path in a first direction includes an ink nozzle for generating and projecting drops towards said record medium, a charging electrode for applying selectively electrostatic charges to drops formed at said nozzle in accordance with the desired locations of the drops on the record medium and an electric field for deflecting the drops to such locations in accordance with the charges thereon; the electric field is produced between a pair of spaced electrodes wherein an effective electrode portion of one of the electrodes is offset in the direction of movement of the record medium with respect to an effective electrode portion of the other; the resulting electric field is curved in the direction of movement of the record medium to compensate for aerodynamic and coulomb forces acting on the charged ink drops which tend to cause lines printed by ink drops deflected in a direction generally perpendicular to the direction of movement of the record medium to be curved in the opposite direction; drops passing through the curved electric field tend to be deflected along the field lines thereof and accelerated toward the record medium in the direction of movement thereof.

United States Patent 1191 Keur et al.

[ July 15, 1975 CONTROL OF DROP PRINTING [75] Inventors: Robert Keur, Niles; Joseph James Stone, Northbrook, both of 111.

[73] Assignee: A. B. Dick Company, Chicago, Ill.

[22] Filed: July 29, 1974 [21] Appl. No.: 492,440

[52] US. Cl 346/1; 346/75 [51] Int. Cl. GOld 15/18 [58] Field of Search 346/75, 1

[56] References Cited UNITED STATES PATENTS 3,681,778 8/1972 Keur 346/75 3,769,631 10/1973 Hill et al. 346/75 OTHER PUBLlCATlONS Gamblin et al., Orthogonolization of Electrostatic Printing, lBM Tech. Disc. Bulletin, Vol, 11, No. 10, March, 1969, pp. 1292-4293.

Primary Examiner-Joseph Hartary Auorney, Agent, or FirmRonald J. LaPorte; Peter S. Lucyshyn [57] ABSTRACT A high speed ink jet printing apparatus for printing on a record medium moving along a path in a first direction includes an ink nozzle for generating and projecting drops towards said record medium, a charging electrode for applying selectively electrostatic charges to drops formed at said nozzle in accordance with the desired locations of the drops on the record medium and an electric field for deflecting the drops to such locations in accordance with the charges thereon; the electric field is produced between a pair of spaced electrodes wherein an effective electrode portion of one of the electrodes is offset in the direction of movement of the record medium with respect to an effective electrode portion of the other; the resulting electric field is curved in the direction of movement of the record medium to compensate for aerodynamic and coulomb forces acting on the charged ink drops which tend to cause lines printed by ink drops deflected in a direction generally perpendicular to the direction of movement of the record medium to be curved in the opposite direction; drops passing through the curved electric field tend to be deflected along the field lines thereof and accelerated toward the record medium in the direction of movement thereof.

6 Claims, 6 Drawing Figures CONTROL OF DROP PRINTING BACKGROUND OF THE INVENTION This invention relates generally to ink jet printing apparatus and more particularly to the deflection electrode assembly employed therein for deflecting charged drops of ink toward predetermined locations on a record medium, and a method for controlling the deflection of such ink drops.

In an ink jet printing system, drops of ink emitted from a nozzle are charged electrostatically in accordance with information corresponding to the desired location of the drops to be deposited on a record medium. The drops are thereafter deflected to such predetermined locations on the record medium by means of a constant electric field.

The drops are deflected in a first direction (normally vertically) while the record medium moves past the nozzle along a path substantially perpendicular thereto (normally horizontally). The electric field is provided usually by an electrode assembly including parallel spaced electrode plates disposed generally in the direction of movement of the record medium.

When it is attempted to print with a system of the above described type at high speeds, such as, for example, greater than about I inches per second, so that the record medium is moved past the ink nozzle rapidly, drops charged sequentially to produce a line extending in the first direction on the record medium tend to form a slanted line. This slant caused by the increased velocity of the record medium, can be removed by rotation of the deflection electrodes which adds velocity to the drops comprising the line in the direction of motion of the paper.

In addition to the latter, a non-linear time difference between drops occurs which causes lines formed in the first direction on the record medium to be curved. The non-linear time difference is produced by aerodynamic and coulomb forces acting on the drops in flight. This produces poor quality printing and becomes a disadvantage especially in printing bar codes. The curvature of these lines cannot be corrected by rotation of the deflection electrodes. A reshaping of the high voltage field is required to overcome the curved line effect.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide in a high speed ink jet printing apparatus, a new and improved deflection electrode assembly which reshapes the electric deflection field to minimize any curvature in lines produced with such apparatus in a direction substantially perpendicular to the direction of movement of the record medium.

It is another object of the present invention to provide a deflection electrode assembly of the above described type which is relatively simple in construction, easily fabricated and effective in operation.

It is still another object of the present invention to provide a method for reshaping the electric deflection field in a high speed ink jet printer apparatus which minimizes the curvature in lines produced by the apparatus in a direction substantially perpendicular to the direction of movement of the record medium.

Briefly, a preferred embodiment of the deflection electrode assembly according to the invention for use in a high speed ink jet printer wherein a record medium is moved along a horizontal path and ink drops are deflected vertically, includes upper and lower spaced electrodes. The lower ground electrode perferably takes the form of a plate extending generally along a horizontal plane adjacent the flight path of the charged ink drops. The upper electrode extends in a second horizontal plane on the opposite side of the drop path, in the direction of the lower plate electrode. An effective portion of the upper electrode is positioned at a predetermined location, offset in the direction of movement of the record medium with respect to an effective lower electrode portion. An effective portion of the upper electrode can be defined by a section of a second plate with only that portion positioned predeterminedly with respect to an effective portion of the lower plate, an edge of a plate or a second plate positioned at an angle with respect to the lower plate. Other suitable electrode configurations are possible as well.

High voltage is applied to the upper electrode. A resulting effective electric field between the effective upper and lower electrode portions is curved in the direction of movement of the record medium as it approaches the upper electrode. The resulting curved field causes drops passing therethrough to be accelerated non-linearly according to the charge thereon in the direction of movement of the record medium so that vertical lines created with the printer apparatus are straight along the entire lengths thereof. In actuality the drops receive from the curved electric field a horizontal component of velocity, non-linearly according to the charged state of the drops; i.e. the higher the charge, the greater the horizontal component of velocity applied, which causes them to track the record medium and impart thereon in a substantially straight line. The proper curvature of the field is determined in accordance with the compensation necessary to obtain straight vertical lines when considering variables, such as record medium velocity, coulomb forces between drops, aerodynamic forces on drops, drop spacing, etc. Such determination can be made easily by one skilled in the art.

DESCRIPTION OF THE DRAWINGS In the drawings FIG. 1 is a diagrammatical representation of a highspeed ink jet printer apparatus wherein a prior art deflection electrode assembly is employed;

FIG. 2 is a cross-sectional view of the prior art electrode assembly of FIG. 1 taken along the line 2-2;

FIG. 3 is a pictorial representation of a record medium illustrating a series of curved vertical lines produced with an ink jet printer apparatus having a deflection electrode assembly of the type shown in FIGS. 1 and 2',

FIGS. 4 & 5 are diagrammatical representations of improved deflection electrode assemblies according to the invention which provide a modification of the electric deflection field to minimize the curvature of lines printed on a record medium with drops deflected in a direction substantially perpendicular to the direction of movement of the record medium; and

FIG. 6 is a pictorial representation of a record medium illustrating a series of lines printed with a highspeed ink jet printer with ink drops deflected in a direction substantially perpendicular to the direction of movement of the record medium, wherein the electric deflection field has been modified according to the invention.

DETAILED DESCRIPTION Referring now to the drawing in greater detail wherein like numerals have been employed throughout the various views to designate similar components, there is illustrated in FIG. 1 a high-speed ink jet printing system designated generally by the numeral 10. The system includes the usual ink nozzle I2 which is connected to an ink reservoir 14. The latter provides ink, under pressure to the nozzle. Drops 16 of ink are generated at the nozzle outlet 18 by vibrating the nozzle at a predetermined frequency determined by an ultra sonic signal applied from a signal source 19 thereto. The drops 16 are projected toward a record medium 20 being transported past the nozzle. Conventionally, as is the case with the system I shown, the record medium is moved horizontally. In FIG. I the record medium is moving out of the page toward the reader. The speed of printing in the case of a high-speed ink jet printing apparatus of the type illustrated is usually greater than 120 inches per second.

As the drops 16 are formed at the nozzle outlet I8, they are selectively charged electrostatically by means of a charging electrode assembly 22. The charges as applied to the drops are produced in accordance with information supplied to the charging assembly from video information circuitry 24. This information determines the desired location of the drops on the record medium to form a desired character.

Subsequent to applying the electrostatic charges to the drops, the drops pass through an electric deflection field 32 created by a deflection electrode assembly 30. The deflection electrode assembly 30, as shown in FIGS. I and 2, is of the type used in the prior art and comprises a pair of similarly dimensioned. parallel, spaced electrode plates 26, 28. An electric field 32 is produced between the plates for deflecting the charged drops vertically in accordance with the charges on the drops, to predetermined locations on the record medium. It should be noted that the electric field 32 produced between plates 26,28 extends along substantially straight vertical lines and as such drops deflected therein are deflected substantially along a vertical path.

In most instances, all drops will not be used to print characters and as such some, when produced, receive no charge. Consequently. they are not deflected when passed through the electric field but instead are di rected to an ink drop catcher 34 from which they are recirculated to the ink reservoir 14 by suitable means (not shown).

In operation. drops generated at nozzle outlet 18 are charged in accordance with the position they are to occupy on the horizontally moving record medium as determined by the video signal applied from circuit 24. The drops pass through the electric field 32 and are deflected accordingly in the vertical direction to such positions on the record medium. Conventionally, drops are deposited sequentially, on a line-by-line basis printing from the bottom of the record medium, upwardly to form a character thereon, the earlier formed drops making up the lower portion of the line and the later formed drops the upper portion thereof. In the case of bar code printing as shown in FIGS. 3 and 6 of the drawing, each line forms a character.

In the case of high speed printing, if the speed of the record medium is greatly increased, drops forming a vertical line which are emitted from the nozzle last in the sequence, will arrive at the record medium at a time later than those initially emitted and slanted lines will be produced. The slant of the lines, is caused by a linear delay in the inpingement of the drops on the record medium making up the vertical line due to the increased speed of the record medium. As mentioned heretofore, this can be overcome merely by application of the known technique of rotating the plates predeterminedly in the direction of movement of the record medium to compensate for the increased speed of the record medium. It will be assumed therefore that the slanted line presents no problem and as such no further discussion of elimination of the slant will be made. Also, for simplicity, the presence of the slant in the vertical lines has been disregarded and, as such, the plate electrodes have been shown in the drawing mounted along horizontal planes rather than in a rotated position.

Because of a non-linear time difference of arrival of drops at the rapidly moving record medium due to aerodynamic and coulomb forces acting on drops formed and projected sequentially toward the record medium, the drops ejected from nozzle outlet 18 arrive at the record medium so that they are deposited along a curved line. As such, vertical lines produced will appear as shown in FIG. 3, curved in the direction opposite from that in which the record medium is moving (see arrow for direction of movement of record medium).

To overcome the latter, it has been found that curving the electric deflection field appropriately in the opposite direction; i.e., in the direction of movement of the record medium, will minimize and most likely eliminate such curved lines.

To provide such a curved field according to the invention, a rearrangement and/or change in the shape of at least one of the electrodes comprising the deflection electrode assembly is made. Other suitable modifications in the electrodes and/or positioning thereof with respect to one another to produce an appropriately curved field can be made as well. Such modifications will be apparent to one skilled in the art. It is intended that these changes be included within the scope of this present invention.

Referring now to FIGS. 4 and 5 of the drawing, there is illustrated therein, as examples, two modified electric deflection electrode assemblies 30a, 30b, respectively, for producing the curved deflection field described according to the invention.

As shown in FIG. 4, the electrode assembly 300 includes a pair of electrodes 26a, 28a, each of which comprises a generally horizontally disposed plate. The plates are separated from each other so that they are positioned on opposite sides of the ink drop path, illustrated by drops 16 moving into the page.

The lower electrode plate 26:: is positioned at a predetermined location with respect to the ink drop path and connected to ground potential. The upper electrode plate 28a is also positioned at a predetermined location with respect to the ink drop path. The upper electrode is offset in the direction of movement (see arrow) of the record medium 20 with respect to the lower electrode so that effective electrode portions X and Y of the lower end upper electrodes, respectively.

are out of vertical alignment with respect to each other;

i.e., the left portion of the lower electrode as seen in the drawing comprising the effective electrode portion of electrode 26a (designated X) and the edge or left end portion of the upper electrode 28a (designated Y), forming the effective electrode portion of the upper electrode are not aligned vertically, the upper effective electrode portion (Y) being offset in the direction of movement of the record medium with respect to the lower effective electrode portion (X).

The result when applying a high voltage potential to the upper electrode 28a, is an electric field 32a formed in the path of drops 16 and curved in the direction of movement of the record medium. The drops 16 passing through the curved field 32a tend to be deflected along the curved electric field lines shown and are accelerated toward the record medium in the direction of movement thereof. The curved field which causes the drops to be moved as described compensates for the aerodynamic and coulomb forces acting on the drops which would otherwise cause the drops to reach the record medium at a later time and form lines curved in a direction opposite from the movement of the record medium, such as shown in FIG. 3. The resulting lines produced when using the curved field 32a according to the invention are straight (See FIG. 6).

Another embodiment b of a modified electric deflection electrode assembly according to the invention is shown in FIG. 5 ofthe drawing. Herein the deflection electrode assembly 30b comprises lower and upper electrode plates 26b, 28b, respectively. As in the case of the electrode assembly of HG. 4, each of the plates is positioned on an opposite side of the ink drop path. Lower electrode plate 26b is grounded and located in a generally horizontal plane, generally parallel to the direction of movement of the record medium. The upper electrode plate 28b is spaced from the lower plate 26b and is positioned at an angle with respect to the plane of the upper electrode. The end 36b of the upper electrode plate is nearer plate electrode 26b than the opposite end 38b of the plate. Thus, effective electrode portions (designated T) of the upper electrode 26b are, as in the embodiment of FIG. 4, offset with respect to effective electrode portions (designated K) of the lower electrode 28b. Therefore, upon the application of a high voltage potential to the upper electrode, a resultant electric field 32b is produced, curved in the direction of movement of the record medium 20. Therefore, ink drops 16 passing along a path through the curved field, as with electric field 32a produced with the deflection electrode assembly 300 of FIG. 4, tend to be deflected along the curved electric field lines illustrated and are accelerated toward the record medium in the direction of movement thereof. The acceleration of the drops as described minimizes or eliminates any curvature in vertical lines formed on the record medium due to the aerodynamic and/or coulomb effects between drops 16.

Of the two embodiments of deflection electrode assemblies shown and described, 30a is preferred because of the uniform distance between electrodes over the extent thereof which permits maximum vertical deflection of drops 16 throughout the electric field 32a.

While the preferred embodiments of deflection electrode assemblies according to the invention are shown for use with a record medium moved horizontally so that ink drops used for printing thereon are deflected toward the medium vertically, such embodiments are not restricted to such orientation.

Other deflection electrode assembly embodiments besides those depicted herein are as mentioned heretofore, possible for producing the desired curved field effect which compensates for the non-linear forces applied to ink drops in high speed ink jet printing apparatus to eliminate curved lines. Such arrangements may include a lower plate electrode and an upper rod or the like electrode, offset with respect to the effective portion of the lower electrode in the direction of movement of the record medium. Such other electrode arrangements will also be obvious to one skilled in the art. It is contemplated to cover in the appended claims any and all such electrode arrangements which fall within the scope of this invention.

We claim as our invention:

l. The method of high speed printing with ink drops on a record medium moving along a path in a first direction, comprising the steps of: generating and projecting ink drops along a path toward said record medium whereat said drops are to be received at predetermined locations to print predetermined characters. charging selectively said ink drops generated and projected toward said record medium in accordance with said predetermined locations to be occupied by said drops on said record medium and providing an electric deflection field in the path of said ink drops for deflection thereof to said predetermined locations on said record medium as determined by the charges on said drops, said field being curved in the direction of movement of said record medium whereby drops passing therethrough for deflection tend to be deflected along the curved electric field lines of said electric field and accelerated toward said record medium in the direction of movement thereof.

2. A high speed ink jet apparatus for printing on a record medium mounted for movement along a predetermined path adjacent said apparatus in a first direction, including in combination: ink drop generating and projecting means for generating ink drops and projecting them along a path towards said record medium whereat said drops are to be received at predetermined locations, ink drop charging means located adjacent said ink drop generating and projecting means for selectively charging said ink drops projected therefrom according to said predetermined locations to be occupied by said drops on said record medium, deflection electrode means interposed between said ink drop charging means and said record medium for providing an electric field in the path of said charged drops for deflecting said drops in a direction generally perpendicular to the direction of movement of said record medium, said electrode means including first and second electrodes positioned in spaced relation on opposite sides of said ink drop path, said electrodes each including an effective electrode portion, the effective electrode portion of one of said electrodes being offset with respect to the effective electrode portion of the other electrode in the direction of movement of said record medium, and high voltage means coupled to said electrodes to provide between said effective electrode portions through said ink drop path, an electric field curved as said field approaches said one effective electrode portion in the direction of movement of said record medium, whereby ink drops passing through said curved field for deflection tend to be deflected along the curved field lines and are accelerated toward said record medium in the direction of movement thereof.

3. lnk jet apparatus as claimed in claim 2 wherein said first electrode comprises a plate extending generally along a plane in said first direction with at least one section of said plate comprising said effective electrode portion and said second electrode being spaced from said plate in a direction perpendicular to said first direction and offset with respect to said first effective electrode portion in the direction of movement of said record medium to provide said curved electric field for deflecting said drops.

4. Ink jet apparatus as claimed in claim 3 wherein said second electrode comprises a plate with a predetermined section thereof being offset in the direction of movement of said record medium with respect to said LII one section of said first electrode and comprising said second effective electrode portion. whereby said curved electric field is formed between said effective electrode portions for deflecting ink drops passing therethrough.

5. lnk jet apparatus as claimed in claim 4 wherein said predetermined section of said second electrode plate comprises an edge thereof extending generally parallel to the path of said ink drops being projected toward said record medium.

6. ink jet apparatus as claimed in claim 5 wherein said record medium is mounted for movement in a generally horizontal direction and wherein said drops are deflected in a generally vertical direction to said predetermined locations on said record medium. 

1. The method of high speed printing with ink drops on a record medium moving along a path in a first direction, comprising the steps of: generating and projecting ink drops along a path toward said rEcord medium whereat said drops are to be received at predetermined locations to print predetermined characters, charging selectively said ink drops generated and projected toward said record medium in accordance with said predetermined locations to be occupied by said drops on said record medium and providing an electric deflection field in the path of said ink drops for deflection thereof to said predetermined locations on said record medium as determined by the charges on said drops, said field being curved in the direction of movement of said record medium whereby drops passing therethrough for deflection tend to be deflected along the curved electric field lines of said electric field and accelerated toward said record medium in the direction of movement thereof.
 2. A high speed ink jet apparatus for printing on a record medium mounted for movement along a predetermined path adjacent said apparatus in a first direction, including in combination: ink drop generating and projecting means for generating ink drops and projecting them along a path towards said record medium whereat said drops are to be received at predetermined locations, ink drop charging means located adjacent said ink drop generating and projecting means for selectively charging said ink drops projected therefrom according to said predetermined locations to be occupied by said drops on said record medium, deflection electrode means interposed between said ink drop charging means and said record medium for providing an electric field in the path of said charged drops for deflecting said drops in a direction generally perpendicular to the direction of movement of said record medium, said electrode means including first and second electrodes positioned in spaced relation on opposite sides of said ink drop path, said electrodes each including an effective electrode portion, the effective electrode portion of one of said electrodes being offset with respect to the effective electrode portion of the other electrode in the direction of movement of said record medium, and high voltage means coupled to said electrodes to provide between said effective electrode portions through said ink drop path, an electric field curved as said field approaches said one effective electrode portion in the direction of movement of said record medium, whereby ink drops passing through said curved field for deflection tend to be deflected along the curved field lines and are accelerated toward said record medium in the direction of movement thereof.
 3. Ink jet apparatus as claimed in claim 2 wherein said first electrode comprises a plate extending generally along a plane in said first direction with at least one section of said plate comprising said effective electrode portion and said second electrode being spaced from said plate in a direction perpendicular to said first direction and offset with respect to said first effective electrode portion in the direction of movement of said record medium to provide said curved electric field for deflecting said drops.
 4. Ink jet apparatus as claimed in claim 3 wherein said second electrode comprises a plate with a predetermined section thereof being offset in the direction of movement of said record medium with respect to said one section of said first electrode and comprising said second effective electrode portion, whereby said curved electric field is formed between said effective electrode portions for deflecting ink drops passing therethrough.
 5. Ink jet apparatus as claimed in claim 4 wherein said predetermined section of said second electrode plate comprises an edge thereof extending generally parallel to the path of said ink drops being projected toward said record medium.
 6. Ink jet apparatus as claimed in claim 5 wherein said record medium is mounted for movement in a generally horizontal direction and wherein said drops are deflected in a generally vertical direction to said predetermined locations on said record medium. 